CBSE Class 12-science Answered
Once the signal is transmitted by a modulated carrier wave it has to be recovered at the reciever. The modulated carrier signal contains the original message signal but it has to be retrieved. This retrieval of the message signal from the transmitted signal is called detection.
When the signal is received by the antenna, it is first amplified because it generally becomes weak while progagating through large distances.
Next is the detector that comprises of a rectifier and an envelope detector. The rectifier produces an output which gives a signal which only lies above the time axis. The signal below the time axis is truncated. This signal has a very high frequency. To get a smooth output ,which is the message signal ,generally a simple RC circuit is used. The final output from the detector is the message signal which can be further amplified.
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